The present invention relates to a unit circuit suitable for driving a driven element or an electronic element such as an organic light emitting element and a liquid crystal element, a control method thereof, an electronic device such as an electro-optical device, and an electronic apparatus.
Generally, transistors are used for driving electro-optical elements such as liquid crystal elements and organic light emitting diodes (hereinafter, properly abbreviated as “OLED elements”). It is necessary to precisely control the transistors for enhancement in performance and increase of the number of gray scales.
In the past, low-temperature polysilicon (LTPS) transistors were used as such driving transistors. In recent years, amorphous silicon transistors attracted attentions as such driving transistors, because they can be measured with low cost and can easily accomplish uniform characteristics. However, when a voltage having the same polarity such as a positive voltage or a negative voltage is continuously applied to a gate electrode of an amorphous silicon transistor, it is known that the threshold voltage thereof varies. The brightness of the corresponding OLED element varies due to variation in threshold voltage, thereby deteriorating display quality.
This is because the characteristics vary due to influence of accumulated carriers or the like when the carriers are continuously supplied to the transistor. This tendency is remarkable specifically when the amorphous silicon transistor is used as a driving transistor. In order to stabilize the characteristics, there has been suggested a technology of first applying a positive voltage to a gate electrode of a driving transistor and then applying a negative voltage thereto (for example, see “Polarity-Balanced Driving to Reduce VTH Shift in a-Si for Active-Matrix OLEDs”, written by Bong-Hyun You et al., SID Symposium Digest of Technical Papers, USA, Society for Information Display, May in 2004, vol. 35, Chap. 1, pp 272-275 (see FIGS. 3A and 3B)).
However, in the technology, since two driving transistors are required and two capacitive elements are required to correspond to each driving transistor, there is a problem in that the circuit configuration is complex. Specifically, when the number of circuit elements such as transistors and capacitive element increases, the circuit area increases and the aperture ratio decreases.
In the technology, since a negative voltage to be applied to the gate electrode of the driving transistor is supplied independently of the positive voltage, the circuit configuration is complex and a dynamic voltage range is widened. Accordingly, there is a problem in that burden on the circuit or power consumption increases. In addition, current flowing through an OLED is affected by the threshold voltage of the driving transistor.